Personal air samplers are battery powered and bodily worn devices that are used to assess a workers exposure to toxic dusts and gasses.
By way of example, U.S. Pat. No. 6,741,056, issued on May 25, 2004 and incorporated herein by reference in its entirety, describes a personal air sampler in which a constant flow of air is provided regardless of changes in the air flow path. This result is achieved by altering the pump speed as a function of the power taken by the pump. The characteristics of the pump are pre-calibrated to provide a constant that is used together with the square of the voltage appearing across the motor armature coils (applied voltage minus back Emf), which reflects the power currently used, to adjust the motor speed and thus provide a constant flow of air under changing conditions of resistance.
By way of further example, U.S. Pat. No. 4,292,574, issued on Sep. 29, 1981 and incorporated herein by reference in its entirety, describes a personal air sampler with an electric motor that is driven by intermittent full-power pulses. More particularly, a constant selected running speed of the electric motor, with a varying mechanical load, is achieved by intermittently pulsing the motor at full power and comparing the back EMF of the motor, between power pulses, with a selected speed voltage, to accordingly control application of the power pulses. A particular control circuit is therefore described which permits operation of a pocket-sized system, powered by a three cell battery, to achieve substantially constant speed, at normally varying loads, throughout a ten hour period, with back EMFs at selected values between 0.01 volt (motor barely turning) and 2.0 volts (high speed).
While these described personal air samplers work for their intended purpose, the following describes an improved personal air sampler having a high efficiency closed loop control system.